Introduction

Missouri borders eight other states, more than any other state (except Tennessee, which also borders eight). Four of the states share an artificial geopolitical boundary with Missouri: Iowa, to the north; Kansas, to the west; Arkansas, to the south; and Oklahoma, to the southwest. The other four are separated from Missouri by a major river: Nebraska, separated by the Missouri River to the northwest; and Illinois, Kentucky, and Tennessee, separated by the Misssissippi River, to the east and southeast, respectively.

The state has significant faunal and floral elements from each of the cardinal directions. Northern species, such as the Four-toed Salamander (Hemidactylium scutatum) and Wood Frog (Lithobates sylvaticus) established populations in the Ozarks and northeast Missouri during a glacial advance and have persisted into modern times.

The Ozarks are a part of the Interior Highlands, a western extension of the Eastern Temperate Forest region. Brook Salamanders (Eurycea) and Woodland Salamanders (Plethodon) both have representatives in the state that are endemic to the region as well as some species that are more widespread. Also, the majority of Missouri's reptiles and amphibians are considered eastern species.

Western species are also found in the Ozarks and along prairie regions in the western part of the state. The Collared Lizard (Crotaphytus collaris) and Flat-headed Snake (Tantilla gracilis) are found on Ozark glades, while species such as the Great Plains Skink (Plestiodon obsoletus) and Variable Groundsnake (Sonora semiannulata) are found in scattered localities in Missouri but are much more common to the west.

Missouri is also home to the confluence of the three largest rivers in the nation. The Mississippi and Missouri River, both of which form an important natural portion of the state, join together in Columbia Bottoms north of Saint Louis. The Mississippi River then joins the Ohio River, flowing from the east, just across from Mississippi County. The northern 2/3 of the state is drained by the Mississippi or Missouri, but the southern 1/3 is drained by tributaries of the Arkansas River or White River.

Naturally, some species are highly dependent on rivers as a habitat. This includes map turtles (Graptemys) and softshell turtles (Apalone) as well as our large salamanders, the Hellbender (Cryptobranchus alleganiensis) and Mudpuppy (Necturus maculosus), among others. However, there are also some species that appear to be reliant upon the habitat created by the rivers. The Western Foxsnake (Pantherophis vulpinus) appears to be restricted to habitat near the large rivers in the northern part of the state, even though it is not particularly associated with rivers elsewhere in its range. There are also several Great Plains anurans, most notably the Great Plains Toad (Anaxyrus cognatus) and Plains Spadefoot (Spea bombifrons), that appear to rely on cultivated river bottoms along the Missouri River as a proxy to their loose soil habitats in the plains. Read more about rivers and watersheds.

The state is comprised of 114 counties (Figure 1) and the independent city of Saint Louis (which has been combined in the MOHAP project with Saint Louis County for practical reasons). This site contains a page for each county that lists its herpetofauna, a collection summary, and a list of potential new records for the county. Click on a county name in Table 1 (below) or use the clickable county map and click a county map to see the detailed page for that county. A labelled map is also available.

Ecoregions

Figure 2: Level I Ecoregions in Missouri and surrounding states. Click to see a labelled map. Modified from EPA (2003). Base map from National Atlas (2001).

Figure 3: Level II Ecoregions in Missouri and surrounding states. Click to see a labelled map. Modified from EPA (2003). Base map from National Atlas (2001).

Figure 4: Level III Ecoregions in Missouri and surrounding states. Click to see a labelled map. Modified from EPA (2003). Base map from National Atlas (2001).

Figure 5: Level IV Ecoregions in Missouri and surrounding states. Click to see a labelled map. Modified from EPA (2003). Base map from National Atlas (2001).

An ecoregion classification system attempts to define and describe geographic regions that correspond to broad ecosystem patterns, topography, geology, soils, vegetation patterns, and the distributions of plants and animals.
Omernik (1987) described ecoregions (Levels I, II, and III) for the conterminous United States as a hierarchical scheme with Level I corresponding to large regions and Level II and Level III representing successively smaller and more precisely described regions. The Environmental Protection Agency (2003) is coordinating an effort to further subdivide Level III regions into Level IV regions. Nigh and Schroeder (2002) published Level III and Level IV ecoregions for Missouri.

Some amphibian and reptile species follow defined ecoregions closely. For example, the Cave Salamander (Eurycea lucifuga) is neatly confined to the Ozark Highlands (Level III) and found throughout the ecoregion, with the exception of most of the Springfield Plateau (Level IV). Several species found in the southeastern alluvial plain are particularly characteristic and also confined to that area (e.g., Three-toed Amphiuma
(Amphiuma tridactylum) and Southern Watersnake (Nerodia fasciata)).

Finally, many species are more closely associated with a particular natural community or habitat than with a particular ecoregion or natural division. For example, The Flat-headed Snake (Tantilla gracilis) can be found in the Ozark Highlands, Osage Prairie, and Interior River Valleys and Hills but it is restricted to rocky glades.

In general, Level IV ecoregions are too granular to be useful in describing the distributions of Missouri amphibians and reptiles, several Ozark salamander species and many of the coastal plains species being notable exceptions. However, this level of detail is useful to understand natural community distributions on which some species are dependent. It also underscores the importance of looking at border states and across artificial political boundaries to understand distributions within Missouri.

Level I (Figure 2), Level II (Figure 3), Level III (Figure 4), and Level IV (Figure 5) ecoregion maps for Missouri and surrounding states, based on Omernik (1987) and Nigh and Schroeder (2002) are included here. The hierarchy for all levels are included in Table 2 (below). Unfortunately, the authors' coding scheme for Level III is inconsistent, though the names do match. Both authors' codes for Level III are included as a cross-reference. For example, Omernik coded the Ozark Highlands as 8.4.5, but Nigh and Schroeder used 39 for the same region.

Table 2. Ecoregion hierarchy for Missouri, based on Omernik (1987) and Nigh and Schroeder (2002). Those regions marked with an asterisk (*) do not occur in Missouri but are sufficiently close to be of interest to Missouri biologists. Those regions marked with a caret (^) are contained entirely within the state’s borders.

8. Eastern Temperate Forests

8.3. Southeastern USA Plains

8.3.3. Interior Plateau* (71)

71m. Northern Shawnee Hills*

71n. Southern Shawnee Hills*

8.3.6. Mississippi Valley Loess Plains (74)

74a. Bluff Hills

74b. Loess Plains

8.3.2. Interior River Valleys and Hills (72)

72a. Wabash / Ohio Bottomlands*

72d. Upper Mississippi Alluvial Plain

72e. Middle Mississippi Alluvial Plain

72f. River Hills

72g. Southern Ozarkian River Bluffs*

72i. Western Dissected Illinoian Till Plain*

72j. Southern Illinoian Till Plain*

72k. Cretaceous Hills*

72l. Karstic Northern Ozarkian River Bluffs*

8.4. Ozark / Ouachita / Appalachian Forests

8.4.5. Ozark Highlands (39)

39a. Springfield Plateau

39b. Elk River Hills

39c. White River Hills

39d. Central Plateau

39e. Osage / Gasconade River Hills^

39f. Saint Francois Knobs / Basins^

39g. Meramec River Hills^

39h. Current River Hills^

39i. Eastern Ozark Border^

39j. Black River Hills Border^

39k. Prairie Ozark Border^

8.4.6. Boston Mountains* (38)

38a. Upper Boston Mountains*

38b. Lower Boston Mountains*

8.5. Southeast US Coastal Plain

8.5.2. Mississippi Alluvial Plain (73)

73a. Northern Holocene Meander Belts

73b. Northern Pleistocene Valley Trains*

73c. Saint Francis Lowlands

73f. Western Lowlands Holocene Meander Belts

73g. Western Lowlands Pleistocene Valley Trains

9. Great Plains

9.2. Temperate Prairies

9.2.3. Western Corn Belt Plains (47)

47d. Missouri Alluvial Plain

47e. Steeply Rolling Loess Prairies

47f. Rolling Loess Prairies

47h. Nebraska / Kansas Loess Hills*

47i. Loess and Glacial Drift Hills*

47m. Western Loess Hills

9.2.4. Central Irregular Plains (40)

40a. Loess Flats and Till Plains

40b. Osage Cuestas*

40c. Wooded Osage Plains

40d. Cherokee Plains

40e. Claypan Prairie^

Prior to Omernik's ecoregion classification scheme, Thom and Wilson (1980) divided Missouri into natural divisions and sections (Figure 6), roughly corresponding to Level III and Level IV ecoregions, respectively. Although the boundaries are a bit different in some cases, most regions are easily recognized between the two schemes. Thom and Wilson's work is included here, particularly since they used historical names (e.g., Crowley's Ridge) for some regions rather than the more generic terms used by the ecoregion authors. A complete list of Missour's natural division and sections can be found in Table 3.

Figure 6: Natural divisions and sections of Missouri. Key to natural divisions and sections is contained within the main text. Click on the map to see a larger version. Modified from Thom and Wilson (1980). Base map from MSDIS (2009) and MDC (2007).

Table 3. List of Missouri Natural Divisions and Sections.

Glaciated Plains

Western

Grand River

Eastern

Lincoln Hills

Ozark Border

Missouri River

Mississippi River

Big Rivers

Upper Missouri (within Glaciated Plains)

Lower Missouri (within Ozark Border)

Upper Mississippi (north of Saint Louis)

Lower Mississippi (south of Saint Louis)

Osage Plains

Ozark Highlands

Springfield Plateau

Upper Ozark

Saint Francois Mountains

Elk River

White River

Lower Ozark

Mississippi Lowlands

Crowley's Ridge

Lowlands

Rivers and Watersheds

Figure 7: Major rivers and streams in Missouri. Click to see a labelled map. Modified from MDC (2007) and USGS (1994).

Figure 8: Major Missouri watersheds. Click to see a labelled map. Based on data from NRCS (2002). Base map from MSDIS (2009).

Missouri is home to four major river drainages: a) Mississippi River, b) Missouri River, c) Arkansas River, and d) White River, with the latter three ultimately flowing into the Mississippi. Included within these drainages are dozens of larger rivers (Table 4, Figure 7) and hundreds of small streams. Aquatic habitats play an important role in the lives and distributions of several species of amphibians and reptiles. Some species found in the state exhibit distributions that can be better understood by referring to these primary drainage systems rather than terrestrial classification schemes, such as those described above.

Watersheds are defined as the land area drained by a specific river or stream system. Since rivers and streams vary greatly in size and the corresponding land they drain, a watershed classification system normally settles on watersheds that are roughly the same size. One such classification system can be seen in Figure 8. Note that watersheds are naturally hierarchical in nature. For example, the Niangua River watershed is one part of the larger Missouri River watershed, which is itself part of the Mississippi River watershed.

For most terrestrial organisms, drainages or watersheds are often of little consequence and can be ignored. But, for those animals that are restricted to rivers, like the Hellbender (Cryptobranchus alleganiensis), Mudpuppy (Necturus maculosus), or softshell turtles (Apalone), the drainage patterns of the rivers are far more important than terrestrial ecoregions. On plateaus, such as the Ozarks, streams from two different watersheds that are otherwise hardly separated from one another are literally hundreds of miles apart from the perspective of obligate aquatic organisms.

Table 4. Major Missouri rivers and tributaries in Missouri listed in stream order. To avoid confusion, the four drainages are separated though in reality, the Arkansas, Missouri, and White Rivers are all tributaries of the Mississippi. These four primary drainages are in bold.

Mississippi River

Cuivre River

Des Moines River

Fabius River

Middle Fabius River

North Fabius River

South Fabius River

Fox River

Meramec River

Big River

Bourbeuse River

North River

Saint Francis River

Big River

Little River

Castor River

Whitewater River

Salt River

Middle Fork

North Fork

South Fork

Spencer Creek

Wyaconda River

Missouri River

Blackwater River

Blue River

Crooked River

Gasconade River

Big Piney River

Little Piney River

Roubidoux Creek

Osage Fork

Grand River

Big Creek

Chariton River

Mussel Fork

Grindstone Creek

Locust Creek

Medicine Creek

Shoal Creek

Thompson River

Weldon River

Yellow Creek

Little Blue River

Little Chariton River

East Fork

Middle Fork

Moreau River

Nodaway River

Osage River

Little Osage River

Marais des Cygnes River

Maries River

Marmaton River

Niangua River

Pomme de Terre River

Sac River

Bear Creek

Cedar Creek

Little Sac River

Turnback Creek

South Grand River

Platte River

Little Platte River

One Hundred and Two River

Tarkio River

White River

Beaver Creek

Bull Creek

Black River

Current River

Jacks Fork River

Eleven Point River

Spring River

Kings River

James River

Crane Creek

Finley Creek

Flat Creek

Northfork River

Bryant Creek

Swan Creek

Arkansas River

Neosho River

Center Creek

Elk River

Big Sugar Creek

Little Sugar Creek

Shoal Creek

Spring River

Like terrestrial ecoregions, aquatic subregions can be classified in discrete units, based on watershed and hydrological characteristics. Subregions are composed of ecological drainage units, which are major watersheds that
are consolidated based on similarity and proximity (MSDIS 2009).

The ecological drainage units map (Figure 9) shows a somewhat consolidated view of the watersheds map based on those watersheds and other characteristics. It is underlain with unique background colors showing the three broad aquatic subregions in the state. Still more detailed aquatic region classifications are available but often include areas based on very small creeks and their watersheds and are therefore beyond the scope of a study of Missouri's herpetofaunal distributions. Aquatic subregions and their component drainage units can be seen in Table 5 (below).

Naturally, many of the same patterns emerge in both terrestrial and aquatic geographic classifications since the two are not independent of one another. However, aquatic subregions and ecological drainage units can differ from their terrestrial counterparts since most aquatic organisms are confined to watersheds as well as specific habitats. Since many species of amphibians and reptiles are partially or wholly dependent on aquatic habitats, distributions can sometimes be best understood and explained by examining aquatic subregions, ecological drainage units, and even individual watersheds.

Figure 9: Missouri Ecological Drainage Units. Click to see a labelled map. Based on data from MSDIS (2009).